Radio pulse altimeter and object detector



June 24,1947. w. D. HERSHBERGER 2,423,524

RADIO PULSE ALTIMETER AND OBJECT DETECTOR Filed Dec. 26, 1941 0302707.DE'I'.

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TFHAISMI'I'WNG Patented June 24, 1947 RADIO PULSE ALTlll/IETER ANDOBJECT DETECTOR William D. Hershberger, Haddonfield, N. J., assignor toRadio Corporation of America, a corporation of Delaware ApplicationDecember 26, 1941, Serial No. 424,530

UNIT

13 Claims. 1

This invention relates to improvements in radio pulse altimeters andobject detectors, and particularly to a radio pulse system in whichaltitude may be measured and objects detected alternately by meansincluding partly common ap- 5 paratus for a radio pulse altimeter andobject paratus energized by a simple switching means. detector, v

Altitude may be measured by radiating a pulse The invention will bedescribed by referring of radio frequency energy toward the earth and t0the accompanying drawing, which is a scheby timing the interval betweenthe radiation of matic circuit diagram of one embodiment of the thepulse and the reception of the pulse after invention. it is reflectedfrom the earth. For any altitude, Referring to the drawing, a sweepgenerator I the pulse length must be short enough to permit is providedwith a switch SI which connects or the radiation to be completed beforethe recepdisconnects a capacitor 3 to change the frequency tion of thereflected pulse. If the pulse is not of t i ing sweep Volta e e tput ofthe short, the receiver may be blocked or it may be sweep generator isapplied to the horizontal dedifiicult to distinguish the outgoing andincomfleeting elements 5 of a cathode ray indicator 1. ing pulses. Byway of example, a radio pulse will One of the vertical deflectingelements 9 is contravel about 100 feet in 0.1 microsecond and, nectedthrough a switch S2 to ground or to a therefore, a pulse of 0.1microsecond duration will biasing source l l to obtain separate sweepswhich travel 50 feet to a reflecting surface and back 50 distinctivelyindicate the altitude or object. The feet to a receiver by the time theinitial pulse other vertical deflecting'element I3 is connectedradiation is completed. tothe output of the I.-F. amplifier l5 which'mayWhile extremely short pulses are used in altimincludea detector. eters,longer pulses are used to detect objects TheI- a plifier W as tW p tcesbecause, generally, the range for object detection One of thesesources'includes a receiving altimis of the order of 0.1 mile to 100 ormore miles. eter antenna I1 and a 500 mega receiver For objectdetection, a pulse length of 0.5 microand local oscillator l9. The otherof these sources second provides sufficient resolution and permitsincludes a directional'receiving antenna, such the application ofincreased power. Not only are as a half rhombic 21, f Object detection,a the pulse durations difierent for altitude detera 500 me e ye e ow b vr and 10094 mining pulses and for object detecting pulses, oscillator23, The narrow band receiver 23 "is but also the time constants of thereceivers are provided with a switch S3 which ay e used chosen to passonly the component frequencies to bias on the receiver by applying abiasing voltof the two types of pulses. A age from a battery'25 or thelike. The object de- In the practical design of radio pulsegeneratection antenna 2i may include a short circuit tors, it is verydifficult to provide an oscillator S4 for reducing the ant response Whent which will start quickly and stop abruptly; for altimeter is inoperation. example, start and stop in 0.1 microsecond. The Thetransmitter includes a key r W c i difiiculty is due to the high ratioof reactance connected to akeyer amplifier 29. The keyer amtoresistance, which is essential for good oscil- 40 plifier consists oftwo or more thermionic tubes latory characteristics, and the low ratioof I'\/- 3|, 33. The tubes 3| 33 may be connected as actance toresistance, which is required if the shown and may employ circuitelements accordoscillations are to stop abruptly. These opposite ing tothe allowed copending application Serial characteristics cannot beobtained in a single No. 182,418, filed December 30, 1937, by Irvingpulse generator but, by a novel arrangement of Wolff, Patent Number2,403,624, granted July 9, master oscillator and power amplifier, aspro- 1945, o pro t n Apparatus for and posed by the instant invention,the two types of method of pu y The O tpu o the first pulses may beobtained. tube 3| is applied to the grid circuit 35 of a master One ofthe objects of the present invention is oscillator 31. The output of thesecond tube 33 to provide an improved means for measuring altiis appliedto the grid circuit 39 of a power amplitude and for detecting objects,Another object fier M. 'The grid circuit 35 of the master oscilis toprovide an improved means for generating lator is coupled through mutualcoupling MI to Short and l p s of radio frequency e ergythe objectdetection antenna 2|. The anode cir- Another object is to provideimproved means for cuit 43 of the master oscillator is coupled throughmeasuring altitude and for detecting objects by mutual coupling M2 tothe grid circuit 39 of the 2 energizing alternately, at least partially,common elements whereby theweight and power requirements are reduced. Anadditional object is to provide an improved and simplified switchingappower amplifier. The anode circuit 45 of the power amplifier iscoupled through mutual coupling M3 to the transmitting altimeter antenna41.

If the maximum altitude and the maximum object detection ranges aregreatly different, different keying rates will be required. The keyingrate change may be effected by a switch S which connects an additionaltiming capacitor 49 to the timing circuit in the keyer 21. The masteroscillator and the power amplifier are both biased normally to cut-off.When the object detection system is in operation, an additional bias isapplied by way of switch S6 which connects a bias battery 5| to the gridcircuit of the power amplifier 4|. The power amplifier is carefullyneutralized, by capacitors 53, 55 cross-connected between the grids andthe anodes of the power amplifier tubes, to prevent energy from themaster oscillator passing through the blocked power amplifier to thealtimeter antenna 41.

The operation of the system is as follows: When the switches SI, S2, S3,S4, S5 and S6 are set for object detection, the master oscillator isenergized by the keying pulse applied from the keyer amplifier 29. Theradio frequency pulse generated by the master oscillator is applied tothe antenna 2| for object detection and is radiated toward the object tobe detected. The radio frequency pulse cannot reach the altimeterantenna because the additional bias applied through switch S6 blocks thepower amplifier. The sweep generator I, which is synchronized by keyercurrents applied through lead 51, generates a slow sweep voltage whichisapplied to sweep the cathode ray horizontally. The echo pulse receivedon the antenna 2| is applied through the narrow band receiver 23, whichis placed in operating condition by the bias applied, through switch S3and I.-F. amplifier IE, to the vertical deflecting electrodes 9, l3'todeflect the ray horizontally or at a discernible angle to its verticalsweep trace. The sweep trace, as is well known, may be calibrated toindicate the distance of the pulse reflecting object.

When the switches SI, etc., are connected for altitude determination,the object detection antenna isshort circuited and the narrow bandreceiver 23 is biased oil so that the altitude determinin pulse does notaffect the object detecting system. At the same time, the objectdetection system is made inactive, the master oscillator 31 is keyed 'onand a shorter keying pulse is applied to key on the power amplifier 4|.Thus a portion of the master oscillator pulse is amplified andshortened, and is radiated toward the earth. The pulse, after reflectionfrom the earth, is applied by way of the receiving antenna l1, broadband receiver [9 and I.-F. amplifier l5 to the vertical deflectingelements 9, [3 to deflect vertically the horizontal timing sweep whichis moved to a distinctive position by the steady bias applied throughswitch S2. If the maximum altitude is substantially less than themaximum range of the object detection system, the keyer and sweepgenerator rates may be increased by disconnecting the capacitors 3 and49 by means of switches SI and'SS, respectively. 7

Thus the invention has been described as an improved radio pulsealtimeter and object detector. The pulse for object detection is derivedby keying a master oscillator; the shorter pulse for altitudemeasurement is derived by passing the pulse from the master oscillatorthrough a power amplifier which is keyed on for only a portion of themaster oscillator keying time. Since the power amplifier does not haveto start into oscillation and thereafter allow the oscillations to dieout, it is practical to key abruptly on and abruptly off. The reflectedpulses are applied respectively through two radio frequency amplifierchannels and hence to a cathode ray tube indicator upon which the timingsweep voltages are impressed.

The switching may be done manually as desired, or continuously by amotor operating the switches at a rate above the persistence of vision,or by means of electronic switching of the character described in anarticle entitled Some electronic switching circuits, by C. C. Shumard,published May, 1938, in Electrical engineering. Although the transmitterand receiver have been described as connected or coupled directly to theobject detection antenna, it should be understood that the connectionmay include the decoupling means disclosed in copending applicationSerial No. 184,354, filed January 11, 1938, by Wolff and Hershberger,Patent Number 2,401,717 granted June 4, 1946, for improvement inSignalling systems.

In the intermittent operation, very high peak powers may be appliedwithout overloading the tubes. Another advantage is that the poweramplifier may be fully loaded in contrast to the relatively small loadswhich may be applied to an oscillator which has to be started andstopped. If the intermittent operation is at a suitable rate, both thealtimeter and object detection signals may be viewed simultaneously dueto the persistence of the cathode ray tube screen.

I claim as my invention:

1. A radio pulse system for measuring altitude and for detecting objectsincluding means for generating a pulse of radio frequency energy, meansfor radiating said pulse toward an object to be detected, means forreceiving said pulse after reflection, an indicator connected to saidreceiving means for indicating the presence of the object by indicatingthe reception of said pulse, means for amplifying a portion of saidgenerated pulse of radio frequency energy, means for radiating saidamplified pulse toward the earth to measure altitude, means forreceiving said amplified pulse after reflection from, the earth, andmeans including said indicator for indicating distinctively the altitudeby indicating the reception of said amplified pulse.

2. A radio pulse system for measuring altitude and for detecting objectsincluding means for enerating a pulse of radio frequency energy, anantenna coupled to said generating means for radiating said pulse towardan object to be detected, means for receiving said pulse afterreflection from said object, a cathode ray indicator connected to saidreceiving means for in-' dicating the presence of said object byindicating the reception of said reflected pulse, means for amplifying aportion of said generated pulse of radio frequency energy to obtain ashorter pulse of radio frequency energy, means for radiating saidshorter pulse toward the earth to measure altitude, means for receivingsaid ra-j diated shorter pulse after reflection from the earth, andmeans including said indicator for indicating the altitude in terms ofthe reception of said reflected shorter pulse.

3. A radio pulse system for measuring altitude and for detecting objectsincluding a master oscillator for generating a pulse of radio frequencynergy, an antenna coupled to said master oscillator for radiating saidpulse toward an object to be detected, means for receiving said pulseafter reflection from said object, a cathode ray indicator connected tosaid receiving means for indicating the presence of said object byindicating the reception of said reflected pulse, a power amplifier foramplifying a portion of said generated pulse of radio frequency energyto obtaina shorter pulse of radio frequency energy, means for radiatingsaid shorter pulse toward the earth to measure altitude, means forreceiving said radiated shorter pulse after reflection from the earth,and means including said indicator for indicating distinctively thealtitude in terms of the reception of said reflected shorter pulse,

4. A radio pulse system for measuring altitude and for detecting objectsincluding means for generating a pulse of radio frequency energy, anantenna coupled to said generating means for radiating said pulse towardan object to be detected, means for receiving said pulse afterreflection from said object, means for generating a timing sweepvoltage, a cathode ray indicator connected to said sweep voltagegenerator and to said receiving means for indicating the distance ofsaid object by indicating the reception of said reflected pulse as a,function of said sweep voltage, means for amplifying a portion of saidgenerated pulse of radio frequency energy to obtain a shorter pulse ofradio frequency energy, means for radiating said shorter pulse towardthe earth to measure altitude, means for receiving said radiated shorterpulse after reflection from the earth, and means including saidindicator for indicating distinctively the altitude in terms of thereception of said reflected shorter pulse as a function of said sweepvoltage.

5. A radio pulse system for measuring altitude and for detecting objectsincluding means for generating a pulse of radio frequency energy, anantenna coupled to said generating means for radiating said pulse towardan object to be detected, means for receiving said pulse afterreflection from said object, means for generating a timing sweepvoltage, means for altering said timing, a cathode ray indicatorconnected to said sweep voltage generator and to said receiving meansfor indicating the distance of said object by indicating the receptionof said reflected pulse as a function of said sweep voltage, means foramplifyin a. portion of said generated pulse of radio frequency energyto obtain a shorter pulse of radio frequency energy, means for radiatingsaid shorter pulse toward the earth to measure altitude, means forreceiving said radiated shorter pulse after reflection fIOm the earth,and means including said indicator for indicating distinctively thealtitude in terms of the reception of said reflected shorter pulse as afunction of said altered timing sweep voltage.

6. A radio pulse system for measuring altitude and for detecting objectsincluding a master oscillator for generating a pulse of radio frequencyenergy, an antenna coupled to said master oscillator for radiating saidpulse toward an object to be detected, means for receiving said pulseafter reflection from said object, means for generating a timin sweepvoltage, a cathode ray indicator connected to said sweep voltagegenerator and to said receiving means for indicating the distance ofsaid object by indicating the reception of said reflected pulse as afunction of said sweep voltage, a power amplifier for amplifying aportion of said generated pulse of radio frequency energy to obtain ashorter pulse of radio frequency energy, means for radiating saidshorter pulse toward the earth to measure altitude, means for receivingsaid radiated shorter pulse after reflection from the earth, and meansincluding said indicator for indicating distinctively the altitude interms of the reception of said reflected shorter pulse as a function ofsaid sweep voltage.

7. A radio pulse system for measuring altitude and for detecting objectsincluding a master oscillator for generating a pulse of radio frequencyenergy, an antenna coupled to said master oscillator for radiating saidpulse toward an object to be detected, means for receiving said pulseafter reflection from said object, means for generating a timing sweepvoltage, means for altering said timing, a cathode ray indicatorconnected to said sweep voltage generator and to said receiving meansfor indicating the distance of said object by indicating the receptionof said reflected pulse as a function of said sweep voltage, a poweramplifier for amplifying a portion of said generated pulse of radiofrequency to obtain a shorter pulse of radio frequency energy, means forradiating said shorter pulse toward the earth to measure altitude, meansfor receiving said radiated shorter pulse after reflection from theearth, and means including said indicator for indicating distinctivelythe altitude in terms of the reception of said reflected shorter pulseas a function of said altered timing sweep voltage.

8. A radio pulse system according to claim 1 including means fortransmitting selectively pulses derived from either said pulse generatoror said pulse amplifier.

9. A radio pulse system according to claim 1 including means forenergizing said radiating means alternately from said pulse generatorand said pulse amplifier.

10. A radio pulse system according to claim 5 including means forenergizing said radiating means alternately from said pulse generatorand from said means for amplifying a portion of said generated pulse ofradio frequency energy and for altering synchronously said timing.

11. A radio pulse system according to claim 5 including means foroperating alternately said object detecting radiating means and saidaltitude radiating means and for synchronously decreasing and increasingthe pulse rate and the sweep rate.

12. A radio system for measuring altitude and for detecting objectsincluding means for generating a first radio signal, means for radiatingsaid signal toward an object to be detected, means for receiving saidsignal after reflection, an indicator connected to said receiving meansfor indicating the presence of the object by indicating the reception ofsaid signal, means including said generating means for establishing asecond radio signal differing distinctively from said first signal,means for radiating said second signal toward the earth to measurealtitude, means for receiving said second signal after reflection fromthe earth, and means including said indicator for indicatingdistinctively the altitude by indicating the reception of said secondsignal.

13. A radio pulse system for measuring altitude and for detectingobjects including means for generating a pulse of radio frequencyenergy, means for radiating said pulse toward an object to be detected,means for receiving said pulse after reflection, an indicator connectedto said receiving means for indicating the presence of the REFERENCESCITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,248,215 Budenbom July 8, 19412,225,046 Hunter Dec. 1'7, 1940 1 2,207,267 Plaistowe July 9, 1940

